dbus: add dbus activation support

Add support for dbus activation of entity manager.  Enabling dbus
activation consists of a few simple steps:

 - Add an activation configuration in /usr/share/dbus-1/system-services
   that maps the dbus service name to the correct systemd service
 - Add a service alias for the service to be dbus activated.  This
   allows dbus activation to be enabled/disabled independently of
   whether the service is started at boot by systemd[1].

[1]https://dbus.freedesktop.org/doc/dbus-specification.html

Tested: systemctl stop xyz.openbmc_project.EntityManager && busctl tree
    xyz.openbmc_project.EntityManager / works
Change-Id: If7dc7f19a19c0ef59370d899f7f67ad6d11064e0
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/service_files/meson.build b/service_files/meson.build
index 2c4909c..5f7baf8 100644
--- a/service_files/meson.build
+++ b/service_files/meson.build
@@ -14,3 +14,10 @@
         )
     endif
 endforeach
+
+dbus_system_bus_services_dir = dependency('dbus-1').get_pkgconfig_variable(
+    'system_bus_services_dir',
+    define_variable: ['prefix', get_option('prefix')])
+install_data(
+    'dbus/xyz.openbmc_project.EntityManager.service',
+    install_dir: dbus_system_bus_services_dir)